These micropumps may be used notably for the in situ administration of medicaments, the miniaturization of the micropump optionally permitting the permanent implantation thereof into the body. These pumps enable a precise dosage of small quantities of fluids to be injected.
These micropumps are in particular described in the article "A piezoelectric micropump base on micromachining of silicon" by H. van Lintel et al. which appeared in "Sensors and Actuators", No 15, 1988, pages 153-167. These pumps essentially comprise a stack of three wafers, i.e. is a silicon wafer disposed between two glass wafers.
The silicon wafer is etched in order to form a cavity which together with one of the glass wafers defines a pump chamber, an inlet valve and an outlet valve, communicating the pump chamber respectively with an inlet channel and an outlet channel, and a regulating valve. A control element, e.g. a piezoelectric disc, is provided on one wall of the chamber. This piezoelectric disc may by deformed when it is subjected to an electrical voltage which causes deformation of the wall of the pump chamber and hence variation in the volume thereof.
The micropump functions as follows. At rest the inlet and outlet valves are in the closed position. When an electrical voltage is applied the wall of the pump chamber deforms and the pressure increases therein until the outlet valve opens. The fluid contained in the pump chamber is then driven towards the outlet channel. During this phase the inlet valve is held closed by the pressure prevailing in the pump chamber. When, however, the electrical potential is removed or reversed, the pressure therein diminishes. This causes closure of the outlet valve and opening of the entry valve. Fluid is thereby drawn into the pump chamber.
As already indicated above, these micropumps are useful especially for the administration of medicaments. It is therefore important to be able to monitor the correct functioning of these micropumps. Moreover in some cases the pump flow rate may drop considerably, e.g. when bubbles of air are present in the pump chamber, or when the pressure in the exit channel becomes too high.